The invention is particularly concerned with a spring-actuated brake cylinder device of the type comprising a brake piston which is acted on one side thereof by a spring member for exerting a brake-applying force in one axial direction, and on the opposite side thereof, by service brake pressure prevailing in a release pressure control chamber for effecting a partial or total neutralization of the spring force, and wherein the improvement comprises a locking device including a locking element for axially locking the brake piston in a brake release position, when reduction of said service brake pressure occurs at a rate in excess of a certain rate, for actuating said locking element, said locking piston being subjected to the service brake pressure acting thereon in a direction in which the locking device is operated to an unlocked position against means exerting a lock-applying force thereon.
Although the brake cylinder device embodying the invention is essentially intended to be used with pneumatic brake systems for railway vehicles, it can also be used with pneumatic brake systems for highway vehicles and with hydraulic brake systems for any type of vehicle.
Certain brake cylinder devices are already known which comprise a spring-actuated piston capable of acting on a rod connected to a friction brake when the pressure decreases sufficiently in a release chamber. Some of these brake cylinder devices have the more specific function of taking over the task of the service brake when the service pressure prevailing in the release chamber becomes insufficient after service brake activation, said brake cylinder devices being intended to partially or entirely take over the function of the service brake cylinder whose action diminishes. In this case, the spring-actuated cylinder piston must be provided with a locking device which enables it to remain inactive or in a release position when the service pressure is cancelled.
A problem which is difficult to solve is that of providing proper cooperative action between the operation of the locking device and that of the brake piston of the spring-actuated cylinder device. Indeed, the piston can be axially diplaced only if the locking device is either in its unlocked position or in a position in which the locking element is in contact with a part of the brake piston rod having no obstructions such as a shoulder, for example.